Off grid solar heating

I’ve been looking at renewable heat recently, the next priority after decarbonising our electricity supply. There are all sorts of ideas for district heating or hybrid systems out there, but the most inspiring idea I’ve come across so far is the off grid solar furnace. It’s been perfected by a renewable energy pioneer called Henry Red Cloud, who creates community energy solutions and employment opportunities on Native American reservations.

The solar heating system his team install is beautifully simple. A large glass-covered box is fitted to the south side of houses, with a heat absorbing metal plate that collects the warmth from the sun. When a thermostat detects that the air in the box is warmer than the air in the house, a fan switches on and directs it inside through a pipe. The fan is powered by a small solar PV panel on the roof, making the whole system self-contained.

This device reduces resident’s energy bills by around a quarter. Check out Lakota Solar Enterprises for more information, and Mr Red Cloud’s inspiring story.

These systems have been optimised for domestic use, but you won’t be surprised to know that the internet has plenty of advice on how to build a solar air heater for your own use – perhaps to fit to a greenhouse or a garage, or to sit on a sunny windowsill. Stacks of empty tin cans painted black seem to be popular.

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6 comments

This sounds good Jeremy, thanks. My other half wants solar powered electricity even though, in our particular position, they would never repay us. I once (maybe 2 yrs ago), came across an american invention which magnified the suns rays so that much less space was required (and no need to convert ones roof). The plans were available for as little as about £35. We are not particlarly DIY’ers (at least not with electrucal inventions), and weren’t sure about getting the required materials, so it’s been left. I can’t even remember what it was called and seem to have lost my notes on it. Do you know anything about this invention? If you do, or, find out at some time, please put in on your site.

Hmm, I haven’t heard of that. and I’m trying to imagine how it would work… Let me know if you come across it again!

I understand the problem with position. Our house is west facing and until very recently, solar companies would advise against solar. The efficiency of panels has improved so dramatically in the last couple of years that west facing roofs are now viable, and I’ve seen other people locally who have had them fitted. So depending on when you last looked into it, it might be better than you think.

Of course, if you’re shaded by trees, that’s trickier, unless you’ve got a garage or a shed or patio that you could place them on instead of the roof.

I’ve built one, and it was pretty easy. I’m skeptical of the black tin cans option, but the glass (or in my case, plastic sheet) covered black box works pretty well. It (combined with some extra insulation in the roof) has raised my house’s temperature by about 2.5 C, and I think there are further improvements that can be made.
Details here: http://guesstimatedapproximations.blogspot.com/2015/05/winter-warmth.html
Cheers, Angus

Yes, you still need the glass as well as the cans, but the glass would be the more important bit I imagine. Thanks for the link – good to hear from someone who can testify first-hand to the idea’s usefulness.